I. Field of the Invention
The present invention relates to bearing assemblies and, in particular, to a self-aligning bearing assembly.
II. Prior Art
Various types of bearings and bearing assemblies are generally known in the art. These bearings and bearing assemblies generally allow a first movable member such as a shaft to move relative to a second member such as a frame. In the area of gas turbine engines and, in particular, gas turbine engines having a forward fan, an engine generally comprises a main shaft having the turbine blades attached at a rear end thereof. The main shaft generally communicates from the rear end to a forward end of the engine having a gear box. A second shaft is provided which generally exits the gear box and communicates with the fan or a propeller of the engine. Appropriate reduction gears are provided in the gear box to reduce the number of rotations of the second shaft relative to the number of rotations of the first main shaft.
In the past, the first main shaft or power shaft was at least partially supported by a bearing or bearing assembly located proximate the gear box. However, due to such factors as manufacturing tolerances and thermal distortions, the first main shaft is often not properly aligned with the reduction gears in the gear box. This generally produces an improper load sharing affect on the gears and teeth of the gears in the gear box, thus reducing gear life and generating a cocking moment in the reduction gears which generally increases rapid gear wear.
Various bearings and bearing assemblies used in the gas turbine engine technology can be found in the following U.S. Patents: U.S. Pat. Nos. 2,659,637; 3,910,651; 3,897,985; 2,440,720; 3,845,999; 3,890,780; 3,853,432; 3,748,058; 4,557,664; 3,237,400. However, none of these references teach an acceptable solution to the problem of misalignment within a given clearance and within a maximum dynamic predetermined load on the bearing. Although the problem could be alleviated by removing the bearing or by reducing the spring rate of the bearing housing, the critical speed of the power turbine shaft is dependent on the position and rate of the bearing and its housing.